1. Field of the Invention
The present invention relates to an ink tank to be mounted on an ink jet recording head for recording on a recording medium by discharging ink droplets. More particularly, the invention relates to the ink tank, which is attachable to and detachable from an ink jet recording head of cartridge type.
2. Related Background Art
For the ink jet recording apparatus that records by discharging ink droplets, there has been known the structure in which an ink jet head and an ink tank are formed separately, and put together when used. The ink tank used for the ink jet recording apparatus of the kind retains ink stably in the usual status (non-recording condition), and needs a mechanism for generating appropriate back pressure (negative pressure) on ink in the recording status in order to supply ink to the ink jet recording head stably.
As one of the methods for generating negative pressure, a porous member, such as urethane form, is used as the member (ink absorbent) that generates negative pressure, and the capillary force of the porous member is utilized. As the negative pressure-generating member, there has been known a structure that uses plural fibrous absorbents as disclosed in the specification of U.S. Pat. No. 5,453,771, besides the urethane form. Particularly when olefinic resin is used as the fibrous absorbent, it can be recycled as material when the used ink tanks are collected. Therefore, from the viewpoint of coping with the environmental problems, it has been positively practiced to adopt the ink tank that utilizes the fibrous absorbent as the negative pressure-generating member.
In recent years, the recording speed of the ink jet recording apparatus has been made faster year after year increasingly. Along with this, it has been required to make the speed of ink supply faster from the ink tank to the ink jet head as a matter of course.
Here, when the fibrous absorbent is used as the negative pressure-generating member in particular, it is roughly observed that fibers are arranged in a desired status of distribution, but in accordance with more precious observation, the status of fibrous distribution here is not uniform due to variation of thickness of each fiber, and the gap between each of them or due to errors occurring in the course of manufacturing process. There are different flow resistances against the movement of retained ink that may take place on the portions where the fibers that form the negative pressure-generating member are concentrated thin or thick. Therefore, it tends to be easier to induce ink from the portion where the concentration thereof is thin and the flow resistance is low. This tendency becomes more conspicuous as the ink flow rate becomes faster. As a result, in order to materialize the higher recording speed, the ink, which is retained on the portion where the fibrous concentration of the fibrous absorbent is smaller, is consumed earlier, and the ink flow path is cut off before the ink, which is retained in the portion having the larger concentration of fibrous distribution, is induced. It is then found that there is a fear that recording may be disabled.
Also, along with the wider use of smaller recording apparatuses, there has been developed a small recording apparatus excellent in portability, and for such a smaller recording apparatus, the main body of the recording apparatus is made smaller, and the ink tank used therefor is made smaller accordingly. For the ink tank used for the smaller recording apparatus of the kind, it is required to enhance the ink storage efficiency and use efficiency so as to make the number of ink tank exchanges smaller. Nevertheless, the ink tank of multiple color integration type, having the ink storage of each color being 10 ml or less in particular, has restriction in terms of the space that should be made available for mounting it on a recording apparatus.
Therefore, for example, in order to enhance the ink storage efficiency by making the height of the ink tank larger, it is required to make the capillary force stronger for retaining ink against the gravitation. This necessitates the fibrous concentration is larger in the ink absorbent, and the resultant space for holding ink is made smaller to that extent. Eventually, therefore, the amount of ink that can be retained is made smaller. Also, if it is intended to arrange the structure so as to retain ink without making the capillary force too larger by making the height of the ink tank smaller for the enhancement of the ink storage efficiency, the ink, which is retained in the ink absorbent immediately above the position of the ink supply port, tends to be induced easier than the ink, which is retained near the bottom face of the ink tank in the position away from the ink supply port in the horizontal direction, because the distance to the ink supply port is shorter. As a result, the difference in facility of ink supply becomes greater at higher recording speed due to difference in distance from the ink supply port, thus inviting the deterioration of ink use efficiency more easily.
Further, for the ink tank having the relatively large dimension in the horizontal direction with the height being suppressed as described above, there is a fear when ink is injected from the ink supply port 114 that the injected ink in the process of manufacture may cover the upper face in the position immediately above the ink supply port 114, because the injected ink reaches the upper face of the ink absorbent 161 before ink is injected into the ink absorbent 161 in the position away from the ink supply port 114. If the condition becomes such as this, the air remaining in the ink absorbent 161 cannot be replaced with the air any longer to make it difficult to impregnate ink in the position where the air still remains and ink is yet to be impregnated, thus deteriorating the filling efficiency of ink eventually.